1. Technical Field
The present invention relates to wireless communication, and more particularly, to a method of communication in a wireless communication system comprising a relay.
2. Related Art
Wireless communication systems are widely used to provide various type of communication services such as voice and data. The wireless communication systems are multiple access systems capable of sharing available radio resources and supporting communication with multiple users. For example, the radio resources are time, frequency, codes, transmission power, etc. Examples of multiple access systems include a TDMA (Time Division Multiple Access) system, a CDMA (Code Division Multiple Access) system, an FDMA (Frequency Division Multiple Access) system, an OFDMA (Orthogonal Frequency Division Multiple Access) system, an SC-FDMA (Single Carrier-Frequency Division Multiple Access) system, etc. The TDMA system uses time as radio resources, the FDMA system uses frequencies as radio resources, the CDMA system uses codes as radio resources, and the OFDMA system uses subcarriers and time as radio resources. Furthermore, the wireless communication systems support bidirectional communication. Bidirectional communication can be performed using a TDD (Time Division Duplex) mode, an FDD (Frequency Division Duplex) mode, an H-FDD (Half-Frequency Division Duplex) mode, etc. According to the TDD mode, uplink transmission and downlink transmission are divided by time resources. According to the FDD mode, uplink transmission and downlink transmission are divided by frequency resources. According to the H-FDD mode, uplink transmission and downlink transmission are divided by combination of time resources and frequency resources.
A wireless communication system includes a base station that provides service to a cell which is a certain area. The quality of a signal transmission is affected by a variation of wireless environments in terms of characteristic of wireless transmission technology. Particularly, radio channels vary with time due to various types of scatters and movement of mobile stations. Furthermore, receive power abruptly decreases as a distance between wireless communication subjects increases, and thus the distance is restricted. Accordingly, a mobile station can communicate with a base station when the mobile station is located in the coverage of the base station, in general. As described above, a maximum transmission rate between a mobile station and a base station, throughput of a user in a cell and throughput of the entire cell decrease due to scatters, the moving speed of the mobile station, a distance between transmitting and receiving sides, etc. For example, if the mobile station is located on the boundary of the cell or an obstacle such as a building exists between the mobile station and the base station, the quality of communication between the mobile station and the base station may be poor.
To solve the aforementioned problem, various techniques for compensating for degradation of transmission signals between the base station and the mobile station are introduced to improve a maximum transmission rate and throughput and extend the coverage of the base station. One of the various techniques is introduction of a relay station in a wireless communication system. For instance, LTE (Long Term Evolution)-Advanced that is one of potent candidates of IMT (International Mobile Telecommunication)-Advanced corresponding to a next-generation mobile communication system following third-generation mobile communication systems includes a relay station. The relay station relays signals between a base station and a mobile station. The relay station can extend the coverage of the base station and improve cell throughput.
The relay station has been recently introduced, and thus a legacy mobile station designed without considering the relay station and a new mobile station designed in consideration of the relay station coexist in a wireless communication system including the relay station. Accordingly, a method for maintaining backward compatibility for the legacy mobile station is required.